Paul,

I was reading on AvWeb this morning about testing engine/prop
combinations. What I found interesting was a casual comment by columnist
Marc Cook about his Barrett-built IO-390-X. He wrote, "my engine doesn't
idle for diddly between 900 and 1200 rpm."

Sometimes when we discuss p-port engines, we're worried about rough
idles. Aircraft engines can have similar or worse problems.

Fortunately, the geared reduction drive on an auto conversion makes it
easier to live with a rough idle even if one has to turn up the engine
speed to smooth it out. An engine speed of 2000 rpms is still only 920
rpm at the prop if run through at 2.17 gearbox or only 700 rpms through
a 2.85 gearbox.

Barry Gardner
Wheaton, IL

Thanks to Tracy there was a couple of developements that made the
P-port practical. The firsts was doing away with the clutch coil spring
plate. The 2.85:1 drive which was second.  Back in the
Ross days the gear box would rattle like mad with a 2.17:1
gear box and the spring clutch plate at 1800 engine RPM.

Now Tracy claims he can idle the engine RPM below 1000 giving
a prop RPM of 350 with Tracy's rubber bushing torque isolator.

Mistral has not got the message yet as of OSH:)

BTW Marc Cook is on here and now managing editor of Kit Planes mag.

Paul Lamar ...No rotor no motor.

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